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SPECT-CT Scan

Authors: Dr Geoffrey Soo* Dr Timothy Cain *

What are the prerequisites for having a SPECT-CT scan done?

Referral for a SPECT-CT scan is usually done after consultation between the nuclear medicine specialist and the referrer. The nuclear medicine specialist may consider the SPECT-CT to be helpful in delineating pathology when standard planar gamma camera imaging is difficult to interpret.

What are the absolute contraindications for a SPECT-CT scan?

This study may not be suitable for pregnant women. The benefit versus risk should be discussed with the nuclear medicine specialist.

Women who are breastfeeding and people who are the primary or sole carer for small children may need to make special preparations after the test to stop breastfeeding for a short time and to avoid close contact with young children due to the small amount of radioactivity released for a while after the test. Patients should discuss this with their referring doctor or the nuclear medicine practice where they will have the test for details. See nuclear medicine for further information about the precautions to take with nuclear medicine studies for breastfeeding patients and those in close contact with children.

What are the relative contraindications for a SPECT-CT scan?

Relative contraindications include patients who exceed the weight limit for the SPECT or CT scanner table (this varies depending on the machine but usually at least 150 kilograms). It is best to check with the technologist staff at your nuclear medicine department first. Patients must be capable of voluntarily staying still.

What are the adverse effects of a SPECT-CT scan?

There are no adverse effects of a SPECT-CT scan.

Are there alternative imaging tests, interventions or surgical procedures to a SPECT-CT scan?

Referral for SPECT-CT is usually done after consultation between the reporting nuclear medicine specialist and the referrer. The nuclear medicine specialist may consider the SPECT-CT to be helpful in delineating pathology when standard planar gamma camera imaging is difficult to interpret.

Further information about SPECT-CT scan:

SPECT-CT imaging involves the acquisition of a low dose, non-contrast, non-diagnostic CT (computed tomography) scan immediately prior to SPECT (single photon emission computed tomography) imaging, which uses a rotating gamma camera. It is usually performed in nuclear medicine as an adjunct to standard single plane, gamma camera imaging as a useful problem solving tool for interpretation of difficult imaging.

Post-acquisition fusion of the CT component of the study with SPECT enables more precise anatomical localisation of radiopharmaceutical uptake. The CT also enables correction for artefact which results from some of the emitted ionising radiation travelling through and being attenuated in the patient’s body tissues prior to being detected on the rotating gamma camera.

To enable accurate image fusion, patients must be able to stay still for the duration of the imaging (usually 30-40 minutes). Risks from the additional radiation required from the low dose CT scan are very minimal, notably the dosage using standard low dose CT technique is around 20-25% that of a comparable standard radiology diagnostic CT scan.

The low dose CT is usually accurate enough to detect gross structural abnormalities such as degenerative arthropathy of the joints or spine, large, multi centimetre soft tissue masses, and viscera. Given the lower radiation dose and absence of IV contrast it is not diagnostic for more subtle pathology such as small metastases, non-displaced fractures or intra-abdominal lymph nodes. Notably, whilst anatomic localisation is improved with SPECT-CT fusion, the inherent resolution of the nuclear medicine component of the imaging is not changed.

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